1. Field of the Invention
The present invention pertains to journal bearing assemblies and particularly to high speed bearings. Such a bearing typically supports a relatively rigid shaft, i.e. one with a substantial diameter. Therefore the rubbing speed of the shaft as it rotates is high. To properly support the shaft precluding significant bending thereof, a thin film of a viscous lubricant must be provided between the bearing surfaces.
As the shaft rotates, the friction associated with the shearing of the lubricant film generates high quantities of heat which cause thermal expansion of the shaft and bearing. The expansion of these two parts often disturbs the optimum thickness of the lubricant film which results in further generation of heat. A self-damaging cycle is thus initiated and can ruin the bearing.
The problem may be further complicated if the expansion of the bearing member is not uniform along its length. For example, the journal bearing member may have an annular flange extending radially outwardly, usually adjacent one end of the journal portion. This flange may be used to mount the bearing, and at least a portion of the flange may serve as one component of a thrust bearing. However, the outer area of the flange is so far removed from the site of the heat generation, i.e. the bearing surfaces, that it will be relatively cold in use. Thus the part of the journal portion of the bearing surrounded by the flange may be forced to expand radially inwardly when heated while the part of the journal portion at the other end of the bearing may expand radially outwardly. This destroys the uniformity of thickness of the lubricant film and may result in severe damage to the bearing assembly.
2. Description of the Prior Art
The problems described above have conventionally been solved by increasing the clearance between the shaft and the journal bearing member so that a significant amount of inward expansion of the journal bearing member can be tolerated without serious damage to the bearing assembly. However, this precludes the use of a lubricant film of relatively uniform and optimum thickness so that the rigidity with which the shaft is supported, the load carrying capacity of the assembly, and the general efficiency are all reduced.
The conventional approach also involves attempts to control the temperature of the bearing by forcibly pumping large quantities of lubricant through the bearing. This, of course, is expensive. Another conventional expedient is to provide a relatively deep circumferential lubricant supply groove in the inner diameter of the journal bearing member. However, such a groove tends to allow lubricant to drain from the loaded side of the bearing thereby decreasing the requirement for high pressure pumping of the lubricant through the bearing.